Nature provides a large number of homodimeric proteins and protein domains that fall into families of related proteins. Such proteins and domains often form homodimers with themselves but do not form heterodimers with other family members. On the other hand, heterodimeric or heteromultimeric proteins are often useful. They provide novel therapeutics and research tools. For example, bispecific antibodies (BsAbs) capable of binding to at least two different antigens have significant potential in a wide range of clinical applications as targeting agents for in vitro and in vivo immunodiagnosis and therapy, and for diagnostic immunoassays. In the diagnostic area, BsAbs have been very useful in probing the functional properties of cell surface molecules and in defining the ability of the different Fc receptors to mediate cytotoxicity (Fanger et al. (1992) Crit. Rev. Immunol. 12:101-124, the teachings of which are hereby incorporated by reference.) However, when BsAbs are generated simply by co-expression of multiple components that can interact without specificity, a large number of species are often generated, and it is often difficult to separate the desired species from the undesired species. Therefore, it is desirable to have techniques for efficiently making heteromultimers. It is particularly desirable to generate antibody subunits that form heterodimers preferentially over forming homodimers so that BsAbs can be directly recovered from recombinant cell culture.
Methods for making heterodimeric proteins have been reported. For example, Stahl and Yancopoulos described the use of fusion proteins including two different receptor subunits to form soluble heterodimeric receptors that could bind to a given cytokine in circulation, and thus block the activity of that cytokine (see U.S. Pat. No. 6,472,179). Carter et al. described a “protuberance-into-cavity” approach for generating a heterodimeric Fc moiety (see U.S. Pat. No. 5,807,706).
These existing methods allow constructions of individual heterodimers, but do not provide general techniques for construction of multimeric proteins involving multiple domain interactions. Therefore, there is a need for a general system for designing heterodimeric pairs that can specifically assemble in an environment containing multiple different potential assembly partners.